Australia’s drinking water supply could be permanently secured when every building is required to reduce mains drinking water consumption, with the use of rainwater tanks being an acceptable way to achieve this.
If each of Australia’s 5.5 million separate houses (75 per cent of residential dwellings) installed rainwater tanks of 4,500 litres capacity, this would provide enough indoor water for 75 per cent more houses. If one million homes in Sydney harvested rainwaterand used it to replace mains drinking water, the yield of rainwater would be up to 80 billion litres. This compares with 45 billion litres from the formerly proposed de-salination plant.
Sixty per cent of an average household’s indoor water use in New South Wales and Queensland could be sourced from a 4,500 litre rainwater tank and 40 per cent in the other states, when rainwater is used interchangeably with mains water for all household purposes. Average indoor household water use is 150,000 litres a year.
Using existing laws controlling mains water use, state governments can require every building in Australia, as a water conservation action, to permanently reduce mains drinking water consumption and can allow installing a rainwater tank as a way to comply.
Equity is achieved between all building owners when the requirement is applied at the point of sale: houses in Australia are sold on average every seven years.
Collecting water from roofs is all about downpipes. Building codes for houses require a downpipe for about every 60 square metres of roof. A small, 1,000 litre rainwater tank can be installed at every downpipe or with two or three downpipes linked to achieve the desired tank capacity.
Rectangular or skinny tanks up to a metre wide fit neatly beneath house eaves and provide a solution for collecting water from the entire roof catchment. Their footprint is minimal compared with a standard 4,500-litre (1,000 gallon) tank. Skinny, 1,000 litre rainwater tanks also suit confined industrial spaces.
All Skinny tanks feed into a “manager” tank where the water is pressurised and fed into the building plumbing system. The objective is to empty tanks at the fastest possible rate so that optimally they are empty at the next fall of rain.
Continuity of water supply to the building is assured by automatic transfer to mains water the instant rainwater is exhausted; and,in reverse, automatically returns to the rainwater supply the moment it becomes available.
All building owners have the right to harvest, use and own the rainwater from their roofs for rainwater tanks, but these rights are currently under challenge from state governments. The NSW Government is now claiming to have the right to mandate collection of water from roofs for rainwater tanks for swimming pools. Currently the NSW Government is the only state to require 40 per cent reduction in mains drinking water consumption for new houses.
In the states of South Australia, Queensland and Victoria, they are claiming the right to mandate rainwater collection from roofs for new houses and the right to stipulate the uses of the water. They are doing this by claiming the right to mandate rainwater collection and use of the water by codifying “housing sustainability standards” and then calling-up the standards into law.
The key rights issues are: who has the right to collect rainwater from the roof - is it the building owner or the state? And once collected, who owns the water - the building owner or the state?
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